Erbium dopants are ideal building blocks for large-scale quantum networks because they show robust spin coherence at liquid helium temperature, and provide optical control via a highly coherent transition at a telecom wavelength where loss in optical fibers is minimal.
By embedding the erbium-doped crystals in a high-finesse optical resonator, the efficiency of the spin-photon interface can be increased by several orders of magnitude, which brings the use for practical applications in quantum communication within reach.
Quantum dots are small enclosures of one material inside another one, which confine individual electrons in space much like 'artificial' atoms, whose optical and electrical properties can be adjusted by choosing the quantum dot size and material.
Their strong optical nonlinearities and sensitivity to electrical charges enables optical measurements of electron tunnelling processes, as well as a frequency stabilization of single-photon emitting quantum dots by fast electrical feedback.
High-resolution optical spectroscopy of gases and biological tissues at mid-infrared wavelengths has wide application in life science and medicine, because distinct molecular fingerprints in the absorption spectrum allow for very sensitive detection of trace gases and biological markers.
While quantum cascade lasers are the most prominent coherent light source in the mid-infrared, quantum cascade detectors are their light-sensing counterparts.
Scientific breakthroughs in quantum physics go hand in hand with technological advances that provide more reliable and extreme experiment conditions.
Two of the commonly required tools are frequency-stable coherent light sources and low-noise magnetic field supplies that are compatible with room-temperature applications.